THE INTRODUCTION OF NEW SPECIES. 5 



that therefore the natural sequence of the species by 

 affinity is also geographical. 



4. In countries of a similar climate, but separated 

 by a wide sea or lofty mountains, the families, genera 

 and species of the one are often represented by 

 closely allied families, genera and species peculiar to- 

 the other. 



Geology. 



5. The distribution of the organic world in time is 

 very similar to its present distribution in space. 



6. Most of the larger and some small groups ex- 

 tend through several geological periods. 



7. In each period, however, there are peculiar 

 groups, found nowhere else, and extending through 

 one or several formations. 



8. Species of one genus, or genera of one family 

 occurring in the same geological time are more closely 

 allied than those separated in time. 



9. As generally in geography no species or genus 

 occurs in two very distant localities without being 

 also found in intermediate places, so in geology the 

 life of a species or genus has not been interrupted. 

 In other words, no group or species has come into 

 existence twice. 



10. The following law may be deduced from these 

 facts : Evert/ species has come into existence coincident 

 both in space and time icith a pre-existing closely allied 

 species. 



This law agrees with, explains and illustrates all 

 the facts connected with the following; branches of 



